For connectors being connection components for household and vehicular electronic devices, materials are used in which a Ni or Cu base undercoat plating is carried out on the surface of brass or phosphorus bronze, and an Sn or Sn alloy plating is further carried out thereon. The Sn or Sn alloy plating usually requires properties of low contact resistance and high solder wettability, and there is recently further demanded the reduction of the inserting force in engagement of a male terminal and a female terminal formed by press working of plating materials. On the plating surface in manufacture steps, there is in some cases generated whiskers, which are needle crystals causing problems such as short-circuit, and the whiskers also need to be suppressed well.
By contrast, Patent Literature 1 discloses a silver-coated electric material in which on a base material whose surface layer has a thickness of 0.05 μm or larger from the surface of the base material and is composed of Ni, Co or an alloy thereof. Ag or an Ag alloy is partially coated, and on the exposed base material surface and on the partially coated Ag or Ag alloy layer, In, Zn, Sn, Pd or an alloy thereof is coated in a thickness of 0.01 to 1.0 μm. According to the Patent Literature, it is described that the electric material can maintain the solderability excellent as an electric material and the sustainability of the mechanical electric connection over a long period.
Patent Literature 2 discloses an Sn or Sn alloy-coated material in which a first coating layer of Ni, Co or an alloy containing these is provided on a Cu or Cu alloy base material surface, and a second coating layer of Ag or an Ag alloy is provided thereon, and an Sn or Sn alloy coating layer is further provided thereon. According to the Patent Literature, it is described that there can be provided an Sn or Sn alloy-coated material which exhibits no oxidative discoloration of the surface and little increase in the contact resistance in spite of being used at high temperatures, thus exhibiting good appearance and contact property over a long period.
Patent Literature 3 discloses an Sn or Sn alloy-coated material in which a first coating layer of Ni, Co or an alloy containing these is provided on a Cu or Cu alloy base material surface, and a second coating layer of Ag or an Ag alloy is provided thereon, and a hot-dipped solidified coating layer of Sn or an Sn alloy is further provided thereon. According to the Patent Literature, it is described that there can be provided an Sn or Sn alloy-coated material which exhibits no oxidative discoloration of the surface and little increase in the contact resistance in spite of being used at high temperatures, thus exhibiting good appearance and contact property over a long period.
Patent Literature 4 discloses an electric contact material in which an Ag layer or an Ag alloy layer is coated on one surface of a conductive strip, and an Sn layer or an Sn alloy layer is coated on the other surface. According to the Patent Literature, it is described that there can be provided an electric contact material or an electric contact component exhibiting little deterioration of solderability even if being exposed to the sulfurization environment or the like.
Patent Literature 5 discloses a method for preventing tin whiskers by a pretreatment in which method (a) one of underlayer metal thin films selected from the group consisting of silver, palladium, platinum, bismuth, indium, nickel, zinc, titanium, zirconium, aluminum, chromium and antimony is formed on a plating object, and thereafter, (b) a tin or tin alloy plating film is formed on the underlayer metal thin film. According to the Patent Literature, it is described that in the tin-based film formed to well secure solderability and the like on the surface of a plating object including a copper-based bare surface, tin whiskers can effectively be prevented by a simple operation.
Patent Literature 6 discloses a plating structure obtained by heat-treating a silver plating structure in which a silver plating layer is formed on the surface of a substrate for plating, and a tin, indium or zinc plating layer of a thickness of 0.001 to 0.1 μm is further formed on the surface of the silver plating layer. According to the Patent Literature, it is described that there can be provided a support, for housing light emitting elements, being excellent in heat resistance and exhibiting little decrease in the reflectance due to sulfurization of silver, and a coating method of electric components which provides electronic components hardly undergoing discoloration due to sulfurization, having gloss innate in silver, and having a low contact resistance.